This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 11(1999)-17295 filed on Jan. 26, 1999, the entire content of which is incorporated herein by reference.
The present invention is generally related to lasers. More particularly, the present invention pertains to a method and apparatus for generating plural pulse lights.
Recently, as evidenced by U.S. Pat. No. 5,880,877 issued to Fermann, et al., a short pulse laser has been realized using a fiber laser. In addition, launching a short pulse light into an optical fiber causes a new pulse at a longer wavelength side of the short pulse light. This has been reported by P. Beaud, et al.(IEEE J. of Quantum Electronics vol. 23, Issued 1987, page 1988.
In certain fields and applications, a need exists for plural short pulse lights which are different in wavelength. However, it is quite difficult, if not impossible, to meet this need using the foregoing proposals or a combination of the foregoing proposals.
A need thus exists for a method and apparatus capable of generating plural short pulse lights.
The present invention provides a method and apparatus for generating plural pulse lights by Induced Raman Effect (Raman scattering) when a short pulse light from a short pulse generation device such as a fiber laser source is launched Into a polarization maintaining fiber.
In the present invention, the short pulse light launched obliquely into the polarization maintaining fiber generates in the fiber two polarized components of the light which perpendicularly intersect each other. Alternatively, before launching the short pulse light, the short pulse light can be decomposed into two polarized components of different phase which intersect at right angles. In addition, the launched short pulse light can be of circular polarization or elliptical polarization.
Then, the resulting induced Raman Effect and Soliton Effect relative to each polarized component causes a soliton pulse which is longer in wavelength than the corresponding component, subject to that the incident angle of the short pulse light is inclined to the incident side of the polarization maintaining fiber. Alternatively, the two polarized components of the light which perpendicularly intersect each other can be obtained before the light is launched into the polarized maintaining fiber.
In addition, the polarization maintaining fiber is designed to have a sufficient energy intensity which by the Raman Effect allows each polarized component of the light to cause a longer wavelength short pulse light at a longer wave side of the light.
Thus, two short pulse lights can be obtained with a relatively simply constructed apparatus.
It is preferable to employ a fiber laser source as the short pulse generation device. This fiber laser source is able to emit a short pulse light whose pulse width is on the femtosecond order. However, other devices capable of emitting a short pulse light with sufficient energy intensity can also be employed.
The above mentioned energy intensity is represented as a function of time or a spectrum shape, which means that varying this shape causes a variation of the energy intensity. In other words, the two longer wavelength lights can be generated by way of holding the energy intensity of an area of each of the two polarized components of the light above a threshold value for a particular time duration.